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WO2011059248A2 - Procédé de transmission mu-mimo dans un système lan sans fil - Google Patents

Procédé de transmission mu-mimo dans un système lan sans fil Download PDF

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Publication number
WO2011059248A2
WO2011059248A2 PCT/KR2010/007975 KR2010007975W WO2011059248A2 WO 2011059248 A2 WO2011059248 A2 WO 2011059248A2 KR 2010007975 W KR2010007975 W KR 2010007975W WO 2011059248 A2 WO2011059248 A2 WO 2011059248A2
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WO
WIPO (PCT)
Prior art keywords
sta
mimo
dimension
virtual
information
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/KR2010/007975
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English (en)
Korean (ko)
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WO2011059248A3 (fr
Inventor
석용호
김봉회
이대원
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LG Electronics Inc
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LG Electronics Inc
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Application filed by LG Electronics Inc filed Critical LG Electronics Inc
Priority to US13/509,277 priority Critical patent/US8891653B2/en
Publication of WO2011059248A2 publication Critical patent/WO2011059248A2/fr
Publication of WO2011059248A3 publication Critical patent/WO2011059248A3/fr
Anticipated expiration legal-status Critical
Priority to US14/484,079 priority patent/US9906281B2/en
Ceased legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0452—Multi-user MIMO systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0621—Feedback content
    • H04B7/0632—Channel quality parameters, e.g. channel quality indicator [CQI]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0658—Feedback reduction
    • H04B7/0663—Feedback reduction using vector or matrix manipulations
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/10—Small scale networks; Flat hierarchical networks
    • H04W84/12—WLAN [Wireless Local Area Networks]

Definitions

  • the present invention relates to wireless communication, and more particularly, to a MU-MIMO transmission method in a wireless LAN system.
  • Wireless LAN is based on radio frequency technology, using a portable terminal such as a personal digital assistant (PDA), a laptop computer, a portable multimedia player (PMP), etc. It is a technology that allows wireless access to the Internet in a specific service area.
  • PDA personal digital assistant
  • PMP portable multimedia player
  • IEEE 802.11 improves Quality for Service (QoS), access point protocol compatibility, security enhancement, radio resource measurement, and wireless access vehicular environment. Standards of various technologies such as, fast roaming, mesh network, interworking with external network, and wireless network management are being put into practice.
  • IEEE 802.11n In order to overcome the limitation of communication speed, which has been pointed out as a weak point in WLAN, IEEE 802.11n is a relatively recent technical standard. IEEE 802.11n aims to increase the speed and reliability of networks and to extend the operating range of wireless networks. More specifically, IEEE 802.11n supports High Throughput (HT) with data throughput of up to 540 Mbps and also uses multiple antennas at both the transmitter and receiver to minimize transmission errors and optimize data rates. It is based on Multiple Inputs and Multiple Outputs (MIMO) technology. In addition, the standard not only uses a coding scheme for transmitting multiple duplicate copies to increase data reliability, but may also use orthogonal frequency division multiplex (OFDM) to increase the speed.
  • HT High Throughput
  • MIMO Multiple Inputs and Multiple Outputs
  • OFDM orthogonal frequency division multiplex
  • VHT Very High Throughput
  • IEEE 802.11 TGac which is progressing standardization of VHT wireless LAN system, studies on using 8X8 MIMO and 80MHz or more channel bandwidth to provide throughput of 1Gbps or more are being actively conducted.
  • the VHT WLAN system aims to support aggregated throughput of 1 Gbps or more and obtain throughput of at least 500 Mbps in one-to-one communication between terminals. For this purpose, it is necessary for several STAs to efficiently use a channel at the same time. In order for multiple STAs to efficiently use the channel at the same time, the AP uses a Space Division Multiple Access (SDMA) technique such as multi-user MIMO. That is, several STAs allow simultaneous transmission and reception with the AP.
  • SDMA Space Division Multiple Access
  • an interference problem may occur. For example, assuming downlink (DL) transmission of MU-MIMO, when the first STA receives a frame from the AP, when the second STA also receives a frame from the AP at the same time, the first STA enters the terminal. In the AP, frame transmission for the second STA may act as interference. As a technique for solving such interference problem, beamforming transmission using smart antenna technology can be considered. In the method for reducing interference in MU-MIMO transmission using beamforming, channel estimation and link adaptation procedures and transmission of related control information between the AP and each STA targeted for MU-MIMO transmission Therefore, it is necessary to consider the frame transmission method through this.
  • the present invention has been made in an effort to provide a MU-MIMO transmission method for reducing interference that may occur when a frame is simultaneously transmitted to a plurality of stations in a WLAN system supporting MU-MIMO and a wireless device supporting the same. will be.
  • a multi-user-multi-input multiple output (MU-MIMO) transmission method performed by an AP in a WLAN system may initiate MU-MIMO transmission to a target STA targeted for MU-MIMO transmission. Transmitting a MU-MIMO initiation message indicating that it is to be received, receiving a sounding frame transmitted from the target STA in response to the MU-MIMO initiation message, and beamforming based on channel information obtained from the sounding frame And transmitting data MU-MIMO, wherein the sounding frame includes channel information H virtual between the AP and the STA, which is precoded and virtualized, and a dimension of the H virtual is defined by the AP. It is lower than the dimension of the channel information H between the STA.
  • MU-MIMO multi-user-multi-input multiple output
  • the MU-MIMO start message includes dimension indication information, and the dimension of the H virtual may be determined based on the dimension indication information.
  • Acquiring the H virtual from the sounding frame may be obtained by performing channel estimation based on the sounding frame.
  • Acquiring the H virtual from the sounding frame may be obtained by receiving channel coefficients of the quantized H virtual included in the sounding frame and transmitted.
  • Pre-coding to be applied to the sounding frame may be performed by applying the specific matrix (eigen matrix) obtained by the H SVD (singular value decomposition) to the precoding matrix.
  • Precoding applied to the sounding frame may be performed by applying a matrix consisting of a combination of some row vectors of U H obtained by singular value decomposition ( H SVD) as a precoding matrix.
  • H SVD singular value decomposition
  • the level indication may be at least any one of information indicating the number of Rx antennas virtualization of information and destination STA to indicate the dimension of the information, the H virtual indicative of the level of the difference between the H level and H virtual .
  • a channel sounding method performed by a station in a WLAN system supporting MU-MIMO indicates that MU-MIMO transmission, which is transmitted from an access point (AP), will be started.
  • the H virtual is provided to the AP, and the dimension of the H virtual is lower than the dimension of the channel information H between the AP and the STA.
  • the MU-MIMO start message includes dimension indication information, and the dimension of the H virtual may be determined based on the dimension indication information.
  • Pre-coding to be applied to the sounding frame may be performed by applying the specific matrix (eigen matrix) obtained by the H SVD (singular value decomposition) to the precoding matrix.
  • the level indication may be at least any one of information indicating the number of Rx antennas virtualization of information and destination STA to indicate the dimension of the information, the H virtual indicative of the level of the difference between the H level and H virtual .
  • a station supporting MU-MIMO transmission includes a processor and a transceiver functionally connected with the processor to transmit and receive a frame, wherein the processor includes an access point (AP).
  • the efficiency of MU-MIMO transmission can be improved by reducing interference that can occur when transmitting frames to multiple stations at the same time.
  • FIG. 1 briefly illustrates a configuration of an example of a WLAN system to which an embodiment of the present invention may be applied.
  • 3 schematically illustrates an interference problem that may occur in MU-MIMO transmission.
  • FIG. 4 shows an example of a link adaptation procedure that can be applied in MU MIMO.
  • NDP null data packet
  • FIG. 6 shows an example in which a channel estimation procedure and a link adaptation procedure that can be applied to MU-MIMO transmission are simultaneously performed.
  • FIG. 8 is a diagram illustrating an example in which a beamformed signal transmitted to another STA serves as interference in MU-MIMO transmission.
  • FIG. 9 shows an example of a channel estimation procedure for acquiring channel information in MU-MIMO transmission.
  • FIG. 10 is a message flow diagram illustrating a MU-MIMO transmission method according to an embodiment of the present invention.
  • FIG. 11 shows an example of the MU-MIMO transmission procedure proposed by the present invention.
  • FIG. 13 is a block diagram illustrating a wireless device in which an embodiment of the present invention is implemented.
  • VHT Very High Throughput
  • MU-MIMO multi-user multiple input multiple output
  • the frame transmission method proposed by the present invention can be equally applied even when the transmission or reception of the frame can be performed at the same time, so that each transmission can interfere with each other.
  • FIG. 1 briefly illustrates a configuration of an example of a WLAN system to which an embodiment of the present invention may be applied.
  • a WLAN system includes one or more basic service sets (BSSs).
  • the BSS is a set of STAs that can successfully synchronize and communicate with each other, and is not a concept indicating a specific area.
  • the BSS can be classified into an infrastructure BSS and an independent BSS (IBSS), which is illustrated in FIG. 1.
  • the infrastructure BSS (BSS1, BSS2) is a distribution system connecting one or more STAs (STA1, STA3, STA4), an AP that provides a distribution service, and a plurality of APs (AP1, AP2).
  • System, DS System
  • the IBSS does not include an AP, all STAs are configured as mobile stations, and thus access to the DS is not allowed, thereby forming a self-contained network.
  • a STA is any functional medium that includes a medium access control (MAC) compliant with the IEEE 802.11 standard and a physical layer interface to a wireless medium.
  • MAC medium access control
  • an AP and a non-AP station Non-AP Station
  • an STA that supports ultra-fast data processing of 1 GHz or more and is capable of transmitting / receiving MU-MIMO is called a VHT STA.
  • all STAs included in the BSS are VHT STAs, or both VHT STAs and legacy STAs (eg, STAs according to IEEE 802.11 a / b / g / n std.) Coexist. You may.
  • a portable terminal operated by a user is a non-AP STA (STA1, STA3, STA4, STA6, STA7, STA8), which may simply refer to a non-AP STA.
  • a non-AP STA is a terminal, a wireless transmit / receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal, or a mobile subscriber. It may also be called another name such as a mobile subscriber unit.
  • WTRU wireless transmit / receive unit
  • UE user equipment
  • MS mobile station
  • a non-AP STA that supports ultra-high speed data processing of 1 GHz or more that supports MU-MIMO transmission as described below is referred to as a non-AP VHT STA or simply a VHT STA.
  • the APs AP1 and AP2 are functional entities that provide access to the DS via a wireless medium for an associated station (STA) associated with it.
  • STA station
  • communication between non-AP STAs is performed via an AP.
  • the AP may be called a centralized controller, a base station (BS), a node-B, a base transceiver system (BTS), or a site controller in addition to the access point.
  • BS base station
  • BTS base transceiver system
  • the AP supporting the MU-MIMO transmission as described below is referred to as a VHT AP.
  • the plurality of infrastructure BSSs may be interconnected through a distribution system (DS).
  • DS distribution system
  • a plurality of BSSs connected through a DS is called an extended service set (ESS).
  • STAs included in the ESS may communicate with each other, and a non-AP STA may move from one BSS to another BSS while seamlessly communicating within the same ESS.
  • DS is a mechanism for one AP to communicate with another AP, which means that an AP transmits a radio frame for STAs coupled to a BSS that it manages, or wirelessly when one STA moves to another BSS. It can forward frames or wireless frames with external networks such as wired networks.
  • This DS does not necessarily need to be a network, and there is no limitation on its form as long as it can provide certain distribution services defined in IEEE 802.11.
  • the DS may be a wireless network such as a mesh network or a physical structure that connects APs to each other.
  • MU-MIMO is a method in which each of a plurality of stations having multiple antennas simultaneously transmits and / or receives independent data streams.
  • Downlink (DL) MU-MIMO means that one STA transmits MU-MIMO to a plurality of receiving STAs.
  • one transmitting STA may be an AP and the plurality of destination STAs may be a non-AP STA.
  • a plurality of STAs are paired, meaning that they are paired with a target STA for MU-MIMO transmission
  • a paired STA (paired) STA refers to a STA paired with a transmission target station of MU-MIMO.
  • a channel estimation procedure and a link adaptation procedure are required to transmit a frame through a plurality of spatial streams.
  • Channel estimation may be performed by transmitting a sounding frame and a channel estimation process using the sounding frame.
  • a link adaptation procedure may determine a modulation and coding scheme (MCS) to be used for each spatial stream.
  • MCS modulation and coding scheme
  • the link adaptation procedure requests an MCS value to be used by an STA to transmit a frame, and correspondingly, a receiving STA It may be in the form of responding to the MCS value.
  • an AP intending to transmit a frame transmits an MCS Feedback Request (MRQ) to a receiving STA to determine an MCS value corresponding to a channel condition.
  • the receiving STA estimates the MCS value corresponding to the channel situation in response to the MCS feedback request message and responds to the AP with the estimated MCS value.
  • MCS Feedback Request MRQ
  • an MCS Feedback requester STA
  • MCS Feedback requester MCS Feedback requester
  • MCS Feedback requester MCS Feedback requester
  • the MRQ is transmitted to receive MCS feedback (MFB).
  • MCS feedback MCS feedback
  • the MRQ is transmitted through a link adaptation control subfield of a high throughput control (HTC) field.
  • the HTC field is transmitted in a MAC header of a MAC (Media Access Control) frame in the HT WLAN system.
  • the link adaptation control subfield may further include information indicating whether to request a sounding frame transmission (TRQ) for channel estimation, antenna selection information, an MCS feedback sequence indicator, and the like.
  • the receiving terminal estimates the MCS suitable for the channel situation using the sounding PPDU and responds to the AP with the result of the estimation.
  • the MFB is delivered through a link adaptation control subfield of the HTC field.
  • the link adaptation procedure in the HT WLAN system is basically intended for 1: 1 transmission between one source STA and one destination STA. Therefore, in an environment such as MU-MIMO, there may be a problem in which interference problems that may occur during point-to-multi point transmission are not considered in MCS estimation.
  • a channel estimation procedure and a link adaptation procedure are required in consideration of transmission of a frame to one destination STA may act as interference to another destination STA.
  • the channel estimation procedure and the link adaptation procedure it is necessary to minimize the effect of the frame transmission on the other target STA by reflecting the simultaneous transmission to the other target STA. It is necessary to acquire channel information through channel estimation and link adaptation procedure reflecting the characteristics of the MU-MIMO transmission environment, and to determine the modulation and coding method based on the channel information.
  • 3 schematically illustrates an interference problem that may occur in MU-MIMO transmission.
  • FIG. 3 illustrates a case in which an AP transmits MU-MIMO DL to STA1 and STA2. It is assumed that the AP has two antennas, and STA1 and STA2 each have one antenna, but this is only an example for convenience of description, and the number of antennas of the AP and the STA is limited thereto in the embodiment of the present invention described below. Not.
  • the spatial stream transmitted to STA2 may act as interference to STA1
  • the spatial stream transmitted to STA1 may act as interference to STA2.
  • an AP transmits a plurality of STAs simultaneously through a plurality of spatial streams, and at this time, spatial streams destined for different STAs may act as interference. In order to reduce such interference, it is necessary to pair and transmit STAs having low channel correlation.
  • the STA estimates the MCS and sends MCS feedback to the AP
  • the actual AP is paired with terminals to which DL MU MIMO transmission is performed, that is, a target STA of MU-MIMO transmission. It is necessary to send MRQ message to STAs at the same time. In this case, the MRQ message may be included in the sounding PPDU and transmitted. This is to make the MCS estimation more accurate by reflecting the influence of the spatial streams to other STAs that may act as interference.
  • the MCS value estimated through the link adaptation procedure in the SU MIMO transmission as in the example of FIG. 2 does not adequately reflect the interference caused by the spatial streams directed to other terminals in the MU MIMO environment.
  • FIG. 4 shows an example of a link adaptation procedure that can be applied in MU MIMO.
  • FIG. 4 illustrates the case of DL MU-MIMO transmission
  • this may also be applied to the case of uplink (UL) MU-MIMO transmission.
  • the AP intends to transmit DL MU-MIMO to STA 1, STA 2, STA 3, and STA 4.
  • the AP simultaneously transmits an MRQ message requesting MCS feedback transmission to paired STAs STA 1, STA 2, STA 3, and STA 4.
  • the MRQ message is sent in the sounding PPDU.
  • the sounding PPDU including the MRQ message is transmitted as a sounding PPDU steered by a pre-coding vector configured to be beamformed to each target STA.
  • Each STA estimates the MCS based on the received sounding PPDUs. Since the AP simultaneously transmitted adjusted sounding PPDUs to STA 1, STA 2, STA 3, and STA 4, the STA may reflect interference that may occur due to the spatial stream transmitted to another STA in the MCS estimation. In other words, the STA that estimates the MCS by transmitting the adjusted sounding PPDU can perform the MCS estimation based on the same channel environment as in the subsequent MU-MIMO transmission.
  • the MFB Sequence Identifier value of the simultaneously transmitted MRQ may be the same value. This is for an MCS Feedback Requester (STA) requesting MCS feedback to efficiently manage MCS feedback report MFBs of MU-MIMO transmission destination STAs and to reduce waste of resources in case of individual MFB sequence indicator transmission. .
  • STA MCS Feedback Requester
  • the MFB sequence indicator has the same value, so that the MCS feedback report with the same MFB sequence indicator means that it is an MCS value estimated by each STA paired for MU-MIMO transmission.
  • the MFB sequence indicator may be included in the MAC header and transmitted. In the HT WLAN system, the MFB sequence indicator is transmitted through a link adaptation control subfield and has a value from 0 to 7.
  • the transmission order (MF) of the MFB is included in the MRQ message, and STA 1, STA 2, STA 3, and STA 4 are transmitted. Can transmit the MFB in the transmission order.
  • the AP may broadcast an MCS Feedback Request management action frame after the predetermined delayed time.
  • STAs that receive the MCS feedback request management action frame respond to the MFB to the AP after a predetermined delay time.
  • the MCS feedback request management action frame may include information regarding the MFB transmission order of STAs transmitting the MFB.
  • NDP null data packet
  • NDP means that there is only a PHY header and no PSD Service Data Unit (PSDU).
  • PSDU PSD Service Data Unit
  • a null data frame means only a MAC header and no MSDU (MAC Service Data Unit). Since there is no PSDU in the NDP, there is no MAC header included in the PSDU. However, the address of the source STA and the address information of the destination STA are transmitted in the SA (Source Address) field and the DA (Destination Address) field of the MAC header. Therefore, in order to transmit the NDP, it is necessary to transmit an NDP announcemnet message indicating that the NDP will be transmitted before the NDP transmission.
  • the PPDU transmitted first by the AP is an example of NDP notification message transmission.
  • the PPDU may include an MRQ and an NDP notification message.
  • the NDP notification message is defined by a new management action frame and transmitted through it, or transmitted to the target STA of the NDP by including an indication bit indicating that the NDP will be transmitted in a conventional control frame, management frame, or data frame. Can be sent.
  • the source STA address and the destination STA address of the NDP are indicated by a source address (SA) and a destination address (D) of an NDP announcement frame (or a frame including an NDP announcement message).
  • SA source address
  • D destination address
  • the NDP is a sounding PPDU, and the STA may perform channel estimation based on the NDP.
  • the AP intends to transmit DL MU-MIMO to STA 1, STA 2, STA 3, and STA 4.
  • the AP transmits a frame including an NDP notification message or an NDP notification frame, and then transmits an NDP.
  • the MRQ may be additionally included in the frame including the NDP notification message or the NDP notification frame.
  • the NDP is transmitted to STA 1, STA 2, STA 3, and STA 4 simultaneously. At this time, the NDPs are transmitted to the NDP adjusted according to the precoding vector set toward each receiving STA. Each STA estimates the MCS through the received NDP. Since the AP previously transmitted the NDP to STA 1, STA 2, STA 3, and STA 4 simultaneously, the interference caused by the spatial stream transmitted to the other STA is reflected in the MCS estimation.
  • FIG. 6 shows an example in which a channel estimation procedure and a link adaptation procedure that can be applied to MU-MIMO transmission are simultaneously performed.
  • the AP transmits a TRQ message (TRM) requesting transmission of a sounding frame to MU-MIMO paired STAs.
  • TRM TRQ message
  • the STAs receiving the TRM transmit a sounding PPDU to the AP so that the AP can perform channel estimation.
  • FIG. 6 it is assumed that the UL channel and the DL channel are reversibility in channel characteristics.
  • the AP transmits a TRM to the sounding PPDU and simultaneously sends an MRQ.
  • the sounding PPDU is then a steered PPDU directed to each STA.
  • the STA estimates the MCS and then sends the MFB to the AP.
  • the MFB may be included in the sounding PPDU transmitted by the STA in response to the TRM requested by the AP.
  • the sounding PPDU transmitted by the STA is transmitted as an unsteered PPDU for the AP to perform channel estimation.
  • the AP performs channel estimation through sounding PPDUs transmitted by the STAs.
  • the MCS value responded by the STA may be corrected by reflecting the change of the channel state. If the channel status does not change between the STA and the AP, DL MU-MIMO transmission may be performed using the MCS value replied by the STA.
  • a precoding matrix (or a precoding vector) suitable for beamforming is determined by using channel information between the STA and the AP.
  • a precoding method for MU-MIMO transmission ZF-BF (zero-forcing beam-forming) or BD-BF (block diagonalization beam-forming) may be performed.
  • ZF-BF zero-forcing beam-forming
  • BD-BF block diagonalization beam-forming
  • FIG. 8 is a diagram illustrating an example in which a beamformed signal transmitted to another STA serves as interference in MU-MIMO transmission.
  • the possibility of acting as interference to different STAs has a correlation with the number of receiving antennas of each STA. For example, as shown in the example of FIG. 8, if the STA1 has four receive (Rx) antennas while the AP is beamforming through four transmit (Tx) antennas, the subspace of a signal that the STA1 can receive ( As the subspace increases, a signal transmitted by the AP to STA2 may act as interference. That is, since STA1 has four Rx antennas, the partial space that can be received increases, and thus the signal transmitted to STA2 can be received, which results in interference to STA1.
  • Rx receive
  • Tx transmit
  • the AP may inform the sounding or channel coefficient to inform the AP of the channel information between the AP and the STA, but there is more information to be transmitted in proportion to the number of antennas.
  • the number of STAs paired for MU-MIMO transmission may vary, informing channel information about spatial streams more than the number of spatial streams to be allocated to each MU-MIMO paired STA effectively uses radio resources. It may not be desirable in view.
  • a MU-MIMO transmission procedure that can reduce interference and a sounding method for beam formation that can reduce interference.
  • a sounding procedure may be first performed to obtain channel information (e.g. channel coefficients) between the STA and the AP from STAs that may be subject to MU-MIMO transmission.
  • channel information e.g. channel coefficients
  • the AP acquires the channel information through the sounding procedure
  • the AP receives the sounding frame from the STA and estimates the channel using the received sounding frame and quantizes the channel coefficients from the STA.
  • the method of receiving and obtaining in the form can be used.
  • the sounding signal transmitted by the STA may be precoded and transmitted in advance.
  • the STA may perform a specific reception beamforming or a reception procedure based on the precoding performed at the sounding signal transmission. Receive data transmitted through MU-MIMO. Through this process, the STA can use the Rx antenna under certain constraints, rather than receiving it through all Rx antennas without restriction, thereby minimizing the interference of the data stream MU-MIMO transmitted from the AP to other STAs. .
  • precoding of the sounding signal may be performed by encoding the channel coefficients and transmitting them in the quantized form.
  • FIG. 9 shows an example of a channel estimation procedure for acquiring channel information in MU-MIMO transmission.
  • the AP Prior to MU-MIMO transmission, the AP transmits a message Msg 1 indicating that MU-MIMO transmission will be started for the MU-MIMO transmission target STA (S910).
  • the MU-MIMO initiation primitive of FIG. 9 is an example of a message indicating that MU-MIMO transmission will be started.
  • Msg 1 is transmitted to the MU-MIMO paired STAs, and the STA receiving the Msg 1 knows that data will be transmitted to the MU-MIMO.
  • Msg 1 may include a message (e.g. TRM) instructing the AP to transmit a sounding frame so as to acquire channel information between the AP and the MU-MIMO paired STA.
  • TRM message
  • the STA may transmit a sounding frame to the AP in order to receive data scheduling (S920). At this time, the STA transmits information on all channels so that the AP can know the channel coefficient corresponding to a physical antenna capable of Tx / Rx. In FIG. 9, the STA transmits a sounding frame by transmitting information on all channels to the AP so that channel information of all dimensions can be obtained through channel estimation using the sounding frame received by the AP.
  • the method is taken as an example, this is only an example, and the STA may directly transmit channel information as quantized data.
  • the STA transmits a sounding frame for channel sounding to the AP according to a method of acquiring channel information by channel estimation using the sounding frame described above. Both sounding and sounding methods in which the STA transmits the quantized channel information to the AP in the form of data using the sounding frame.
  • the AP which has acquired the channel information through S920, transmits preformed beamforming MU-MIMO data to the MU-MIMO paired STAs based on the acquired channel information (S930).
  • this MU-MIMO transmission scheme may cause the problem described in the example of FIG. 8.
  • the number of MU-MIMO paired STAs and the number of Rx antennas of each STA there are problems in which waste of radio resources required for signaling for channel information and data streams transmitted to other STAs may act as interference. May result.
  • FIG. 10 is a message flow diagram illustrating a MU-MIMO transmission method according to an embodiment of the present invention.
  • the AP transmits Msg 1 to the MU-MIMO paired STA prior to the MU-MIMO transmission (S1010).
  • Msg 1 is transmitted to MU-MIMO paired STAs, and the STA receiving Msg 1 knows that data will be MU-MIMO transmitted to itself.
  • Msg 1 may include a message (e.g. TRM) instructing the AP to transmit a sounding frame so as to acquire channel information between the AP and the MU-MIMO paired STA.
  • TRM message
  • the STA Upon receiving the Msg 1, the STA transmits a sounding frame so that the AP can acquire channel information (S1020).
  • the sounding is performed without sounding the channel for all the Tx / Rx antennas, but only a part of the sounding.
  • the virtualized channel is sounded by virtualizing the Rx antenna using precoding.
  • the AP may determine that the STAs have fewer Rx antennas than the actual Rx antennas. Therefore, the problem by the number of Rx antennas of the above-described STA can be solved.
  • this method also has the advantage of reducing interference by data streams transmitted to other STAs in an MU-MIMO transmission environment.
  • the above-described sound applied by the STA may be expressed in all dimensions by using precoding (that is, post-precoding when viewed from the receiving AP) in the sounding process. Instead of transmitting channel information, it may be said to transmit channel information of some dimension.
  • the STA performing precoding prior to sounding and transmitting information about the virtualized channel may be referred to as transmitting effective channel information instead of transmitting channel information of all dimensions in other words.
  • the AP receiving the sounding frame obtains channel information of the channel virtualized by the STA (in other words, may be referred to as effective channel information), and beamforms the channel information based on the acquired virtualized channel information.
  • MU-MIMO data is transmitted MU-MIMO (S1030).
  • the transmission of the virtualization channel information having a lower dimension than the actual channel information by the STA may be performed in various ways.
  • a method in which an STA transmits a signal measured by an AP and estimates channel information by using a correlation between a UL channel and a DL channel of a time division duplex (TDD) system the STA transmits a specific matrix (or If the AP transmits a signal for estimating channel information by multiplying the vector, the AP acquires information of the virtualized channel.
  • the AP may operate by determining that the STA has fewer Rx antennas than the number of Rx antennas actually owned by the STA.
  • each MU-MIMO paired STA transmits the sounding frame to which precoding is applied when transmitting the sounding frame to the AP.
  • some column vectors of the matrix U obtained through SVD ( U is an eigen matrix obtained by SVD of the channel matrix H ) may be applied to precoding in sounding.
  • the STA may transmit a sounding frame by applying a precoding matrix determined adaptively to the request of the AP or the channel situation, wherein the AP indicates a dimension that may be a reference in determining the precoding matrix.
  • Information may be informed to the STA.
  • the dimension indication information indicated by the AP may be included in Msg 1 and transmitted or may be transmitted to the STA through a separate management action frame.
  • the dimension indication information may be in the form of direct indication of the dimension of the virtualized channel or a difference value between the dimension of the virtual channel and the virtual channel when the STA virtualizes the channel by applying precoding to sounding.
  • the dimension indication information may be in the form of indicating the number of Rx antennas of the STA seen from the AP point of view as a result of virtualization.
  • the estimated channel coefficient matrix is multiplied by the virtualization matrix to multiply the virtual channel having a smaller dimension.
  • a method of making a virtual channel coefficient matrix and transmitting the corresponding information to the AP may be used.
  • precoding performed before transmission determines that the spatial STA does not receive spatial interference for different spatial streams when receiving a signal from the receiving STA.
  • matrices U and V obtained by SVD of arbitrary matrices are unitary matrices and have the same characteristics as in Equation 1. Where I is the identity matrix.
  • X is a transmission signal to be transmitted
  • P is a transmission precoding matrix
  • N is a noise signal
  • Y is a reception signal.
  • the ⁇ matrix is composed of only simple constants as diagonal matrices. If V is used for transmission precoding and U H is used for equalization on the receiving STA side, the STA receives a data signal multiplied by a constant value. Because it can be obtained from the side, interference between spatial streams can be minimized.
  • Msg 1 eg MU-MIMO start primitive
  • NAVs Network Allocation Vectors
  • Sounding for channel estimation of STAs is generally sounding transmitted without precoding, which makes it possible to estimate the entire channel. At this time, the AP may not transmit the sounding frame.
  • FIG. 11 shows an example of the MU-MIMO transmission procedure proposed by the present invention.
  • the AP transmits the CTS-to-self frame in a legacy format that can be heard by all STAs in the BSS, so that STAs except for the MU-MIMO paired STA that receive the STA can configure NAV.
  • the AP sends an MU-MIMO primitive indicating that MU-MIMO transmission will be started following CTS-to-self frame transmission.
  • the AP may transmit a channel estimation signal (e.g. Long Training Field (LTF)) for sounding a channel between the AP and the MU-MIMO paired STA together with the MU-MIMO primitive.
  • LTF Long Training Field
  • the AP sends the MU-MIMO primitive in legacy format so that all STAs can hear it.
  • An STA that is not a target of MU-MIMO transmission receiving the MU-MIMO primitive may set a NAV to defer channel access. Thereafter, a signal for channel estimation is transmitted in order to sound a channel between the AP and the STA together with the NDP frame after a time corresponding to a short interframe space (SIFS).
  • SIFS short interframe space
  • the wireless device 1300 is a block diagram illustrating a wireless device in which an embodiment of the present invention is implemented.
  • the wireless device 1300 may be an AP or an STA.
  • the wireless device 1300 includes a processor 1310, a memory 1320, and a transceiver 1330.
  • the transceiver 1330 transmits / receives a radio signal, but implements a physical layer of IEEE 802.11.
  • the processor 1310 is connected to the transceiver 1330 to implement the MAC layer of IEEE 802.11.
  • the wireless device 1300 becomes the AP.
  • the wireless device 1300 becomes an STA.
  • the processor 1310 and / or the transceiver 1330 may include an application-specific integrated circuit (ASIC), another chipset, a logic circuit, and / or a data processing device.
  • ASIC application-specific integrated circuit
  • Memory 1320 may include read-only memory (ROM), random access memory (RAM), flash memory, memory cards, storage media, and / or other storage devices.
  • ROM read-only memory
  • RAM random access memory
  • flash memory memory cards
  • storage media storage media
  • / or other storage devices When the embodiment is implemented in software, the above-described technique may be implemented as a module (process, function, etc.) for performing the above-described function.
  • the module may be stored in the memory 1320 and executed by the processor 1310.
  • the memory 1320 may be inside or outside the processor 1310 and may be connected to the processor 1310 by various well-known means.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Power Engineering (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Radio Transmission System (AREA)

Abstract

L'invention concerne un procédé de transmission à entrées multiples, sorties multiples, utilisateurs multiples (MU-MIMO) dans un système LAN sans fil et un dispositif sans fil de prise en charge associé. Selon l'invention, le procédé de transmission MU-MIMO comprend les étapes de : transmission d'un message de déclenchement MU-MIMO qui indique que la transmission MU-MIMO est déclenchée, à une station cible (STA) qui est la cible de la transmission MU-MIMO ; réception d'une trame de sondage transmise depuis la STA cible, en réponse au message de déclenchement MU-MIMO ; et transmission de données dans un mode MU-MIMO par l'exécution d'un processus de formation de faisceaux sur la base des informations de canaux obtenues de la trame de sondage, la trame de sondage comprenant des informations de canaux "Hvirtual " entre une STA et un AP, qui ont été précodées et virtualisées, la dimension des informations de canaux "Hvirtual " étant inférieure à la dimension des informations de canaux "H" entre la STA et l'AP.
PCT/KR2010/007975 2009-11-12 2010-11-12 Procédé de transmission mu-mimo dans un système lan sans fil Ceased WO2011059248A2 (fr)

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US8891653B2 (en) 2014-11-18
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US20150029986A1 (en) 2015-01-29
US20120230443A1 (en) 2012-09-13

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